Numerous attempts have been made to achieve golf balls endowed with both increased carry and a good feel when hit. The approach most commonly taken in solid golf balls has been to alter the hardnesses of the cover and the core.
Solid golf balls having a multilayer solid core with a core inner layer and a core outer layer have recently been proposed. For example, JP-A 23069/1994 discloses a solid golf ball having a three-layer construction comprising a core, a core outer layer, and a cover wherein the core has a diameter of 23 to 35 mm and a Shore D hardness of 30 to 62 The core outer layer has a Shore D hardness of 30 to 56 whereby a suitable spin is maintained and the rebound characteristics and carry are improved. However, when this solid golf ball is hit at a relatively low head speed of about 35 m/s, the ball is given a low initial velocity, failing to have sufficient carry.
JP-A 170012/1994 describes a solid golf ball in which the core inner layer is made of Surlyn ionomer resin, commonly used as a cover material, that has been foamed (.rho.=0.2 to 1.0). Yet, the core inner layer is so soft that the ball provides a poor rebound and an inadequate carry.
Because most conventional golf balls are targeted at professional golfers and skilled amateurs, they have been designed for optimal performance in a relatively club high head speed range of about 40 to 45 m/s. But these golf balls are often less than ideal for use by relatively low club head speed players such as women golfers and seniors who strike the ball at club head speeds of less than 40 m/s. If a low club head speed golfer plays a full shot with a driver, for instance, the speed upon impact (initial velocity) conventional balls acquire will be too low to provide an adequate carry.